1. Field of the Technology
The present disclosure relates to cutting inserts adapted for use in earth-boring bits and in other articles of manufacture.
2. Description of the Background of the Technology
Cemented carbides are composites including a discontinuous hard phase dispersed in a continuous relatively soft metallic binder phase. The dispersed (discontinuous) phase typically comprises transition metal carbide, nitride, silicide, and/or oxide, wherein the transition metal is selected from, for example, titanium, vanadium, chromium, zirconium, hafnium, molybdenum, niobium, tantalum, and tungsten. The binder phase typically comprises at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. Alloying elements such as, for example, chromium, molybdenum, boron, tungsten, tantalum, titanium, and niobium may be included in the binder to enhance certain properties of the composite material. The binder phase binds or “cements” the dispersed hard grains together, and the composite exhibits an advantageous combination of the physical properties of the discontinuous and continuous phases. Although the discontinuous hard phase of such composites may not include metal carbides, the commercially available versions typically include carbides as the discontinuous hard phase. Therefore, the composites are commonly referred to as “cemented carbides” even if carbides are absent or only constitute a portion of the discontinuous hard phase. Accordingly, references herein to “cemented carbides”, both in the present description and the claims, refer to such materials whether or not they include metallic carbides.
Numerous cemented carbide types or “grades” are produced by varying parameters that may include the composition of the materials in the dispersed and/or continuous phases, the average size of the dispersed phase regions, and the volume fractions of the discontinuous and continuous phases. Cemented carbides including a dispersed tungsten carbide phase and a cobalt or cobalt alloy binder phase are the most commercially important of the commonly available cemented carbide grades. Conventional cemented carbide grades are available as powders (referred to herein as “cemented carbide powders”), which may be processed to a final form using, for example, conventional press-and-sinter techniques.
Cemented carbide grades including a discontinuous tungsten carbide phase and a continuous cobalt binder phase exhibit advantageous combinations of ultimate tensile strength, fracture toughness, and wear resistance. As is known in the art, “ultimate tensile strength” is the stress at which a material ruptures or fails. “Fracture toughness” refers to the ability of a material to absorb energy and deform plastically before fracturing. “Toughness” is proportional to the area under the stress-strain curve from the origin to the breaking point. See MCGRAW-HILL DICTIONARY OF SCIENTIFIC AND TECHNICAL TERMS (5th ed. 1994). “Wear resistance” refers to the ability of a material to withstand damage to its surface. Wear generally involves progressive loss of material from an article due to relative motion between the article and a contacting surface or substance. See METALS HANDBOOK DESK EDITION (2d ed. 1998). Cemented carbides find extensive use in applications requiring substantial strength and toughness and high wear resistance. Such applications include, for example, metal cutting and metal forming applications, earth-boring and rock cutting applications, and use in machinery wear parts.
The strength, toughness, and wear resistance of a cemented carbide are related to the average size of the regions of dispersed hard phase and the volume (or weight) fraction of the binder phase present in the composite. Generally, increasing the average grain size of the dispersed hard regions and/or the volume fraction of the binder phase in a conventional cemented carbide grade increases the fracture toughness of the composite. However, this increase in toughness is generally accompanied by decreased wear resistance. Metallurgists formulating cemented carbides, therefore, are continually challenged to develop grades exhibiting both high wear resistance and high fracture toughness, and which are otherwise suitable for use in demanding applications.
In many instances, cemented carbide parts are produced as individual articles using conventional powder metallurgy press-and-sinter techniques. The press-and-sinter manufacturing process typically involves pressing or otherwise consolidating a portion of a cemented carbide powder in a mold to provide an unsintered, or “green”, compact of defined shape and size. If additional shape features are required in the cemented carbide part that cannot be achieved readily by consolidating the powder, the green compact is machined prior to sintering. This machining step is referred to as “green shaping”. If additional compact strength is needed for the green shaping process, the green compact can be presintered before green shaping. Presintering occurs at a temperature lower than the final sintering temperature and provides what is referred to as a “brown” compact. The green shaping operation is followed by the high temperature sintering step. Sintering densifies the material to near theoretical full density to produce a cemented carbide composite. Sintering also develops desired strength and hardness in the composite material.
Rotary cone earth-boring bits and fixed cutter earth-boring bits are employed for oil and natural gas exploration, mining, excavation, and the like. Rotary cone bits typically comprise a steel body onto which cutting inserts, which may be made from cemented carbide or another material, are attached. Referring to FIG. 1, a typical rotary cone bit 10 adapted for earth-boring applications includes a steel body 12 and two or three interlocking rotary cones 13 that are rotatably attached to the body 12. A number of cutting inserts 14 are attached to each rotary cone by, for example, mechanical means, adhesive, or brazing. The cutting inserts, which also may be referred to as “cutting elements”, may be made from cemented carbide or another material. FIG. 2 depicts a number of cemented carbide cutting inserts 22 attached to a surface 24 of an insert holder portion of a fixed cutter earth-boring bit.
Conventional cemented carbide cutting inserts configured for use with earth-boring bits are commonly based on pure tungsten carbide (WC) as the dispersed hard phase and pure cobalt (Co) as the continuous binder phase. While WC—Co cemented carbide cutting inserts provide advantages relative to materials previously used in cutting inserts for rotary cone earth-boring bits, WC—Co inserts can suffer from premature abrasion and wear. Premature wear may necessitate replacement of one or more worn cutting inserts or an entire rotary cone or fixed cutter earth-boring bit, which requires removing the drill string from the borehole. This can significantly slow and increase the cost of the drilling process.
Accordingly, it would be advantageous to develop an improved cemented carbide material for use in cutting inserts for rotary cone, fixed cutter, and other earth-boring bits that exhibits advantageous abrasion resistance and wear life compared with conventional WC—Co cemented carbides, while not significantly compromising cutting insert strength and toughness. More generally, it would be advantageous to provide a novel cemented carbide material for uses including those wherein high abrasion resistance and wear life are desired, and wherein strength and toughness also are important.